Control apparatus for internal-combustion engine with variable valve mechanism

ABSTRACT

An intake variable valve mechanism  34  is provided that allows closing timing of an air intake valve  30  to be varied. The intake variable valve mechanism  34  has a first control mode that controls IVC timing of the intake valve  30  at an angle-advancing side relative to a certain range including an air intake bottom dead center BDC, and a second control mode that controls the IVC timing of the intake valve  30  at an angle-retarding side relative to the certain range. IVC variable control (first control mode) for making the IVC timing of the intake valve  30  variable according to load is selected for operation in a region of relative low loads, and intake valve closing retardation control (second control mode) for controlling the intake valve  30  in fully retarded IVC timing is selected for operation in a region of relatively high loads.

TECHNICAL FIELD

The present invention relates to a control apparatus for an internal-combustion engine having a variable valve mechanism.

BACKGROUND ART

Patent Document 1, for example, discloses a control apparatus for an internal-combustion engine having a variable valve mechanism to make variable the opening and closing timing of an air intake valve and the lift amount thereof. The conventional control apparatus as described in Patent Document 1 is constructed so that when knock is detected, the apparatus executes control to suppress knock and suppress changes in torque. More specifically, as an example of the control performed when knock is detected, the conventional control apparatus operates to increase the opening area of the intake valve as well as to advance the closing timing thereof.

Including the above-mentioned document, the applicant is aware of the following document as a related art of the present invention.

[Patent Document 1] Japanese Patent Laid-open No. 2002-180857

[Patent Document 2] Japanese Patent Laid-open No. 2004-116315

[Patent Document 3] Japanese Patent Laid-open No. Hei 4-246249

DISCLOSURE OF INVENTION

In an internal-combustion engine with a variable valve mechanism for making variable the opening and closing timing of an intake valve and the lift amount thereof, as in the foregoing conventional internal-combustion engine, such intake air amount control as outlined below may take place to reduce pumping loss for improved fuel efficiency. That is to say, the intake air amount may be controlled such that: the closing timing of the intake valve is advanced by reducing the operating angle of the intake valve to limit the amount of air passed through the intake valve, and a throttle angle is correspondingly increased at the same time.

According to the above control of the intake air amount, when an operating region of the internal-combustion engine changes from a low-load region to a high-load region, pumping loss is reduced by gradually increasing the operating angle in accordance with the load required of the internal-combustion engine. As a result, an operating angle equivalent to the very timing in which the intake valve is closed near a bottom dead center will be used in a medium-load region. When the intake valve is closed near the bottom dead center, an actual in-cylinder compression ratio will increase and knock will be more likely to occur.

The present invention has been made for solving the above problem, and an object of the invention is to provide a control apparatus which can control an operating state of an internal-combustion engine while properly avoiding knock in the internal-combustion engine having a variable valve mechanism to make at least closing timing of an intake valve variable

The above object is achieved by a control apparatus for an internal-combustion engine having a variable valve mechanism which at least makes closing timing of an intake valve variable. An intake valve control means is provided with a first control mode for controlling the closing timing of the intake valve at an angle-advancing side relative to a certain range including an air intake bottom dead center, and with a second control mode for controlling the closing timing of the intake valve at an angle-retarding side relative to the certain range. The intake valve control means controls the closing timing of the intake valve in either the first control mode or the second control mode. A control mode selection means is also provided for selecting the first control mode for operation in a region of relatively low loads, and selecting the second control mode for operation in a region of relatively high loads.

In a second aspect of the present invention, at least the first control mode of the first control mode and the second control mode may be the control that determines the closing timing of the intake valve according to a load of the internal-combustion engine.

In a third aspect of the present invention, the second control mode may be the intake valve closing retardation control that determines the closing timing of the intake valve such that even under a steady state, blowback of intake air into an intake passage occurs.

In a fourth aspect of the present invention, the first control mode may be the control that determines the closing timing of the intake valve according to a load of the internal-combustion engine.

In a fifth aspect of the present invention, the intake valve closing retardation control may be used in an operating region in which the engine runs at a speed equal to or smaller than a certain value and under a load equal to or greater than a certain value.

In a sixth aspect of the present invention, the control mode selection means may select the first control mode until the load region of the internal-combustion engine has reached the higher region as engine speed increases.

The seventh aspect of the present invention may include a torque control means for controlling a torque of the internal-combustion engine in addition to controlling the closing timing control of the intake valve via the intake valve control means. A torque control change means may be provided for, when the second control mode is selected by the control mode selection means, changing the torque control performed by the intake valve control means, to the torque control performed by the torque control means.

In an eighth aspect of the present invention, the torque control means may be a throttle valve that controls an intake air amount. And the torque control means may adjust an open position of the throttle valve in accordance with at least the closing timing of the intake valve, of the closing timing and operating angle of the intake valve existing when the first control mode is changed to the second control mode.

The ninth aspect of the present invention may include an ignition timing change means for changing ignition timing of the internal-combustion engine in synchronization with the control mode change between the first control mode and the second control mode.

In a tenth aspect of the present invention, the ignition timing change means may determine an advancing amount of the ignition timing in accordance with a valve overlapping period existing when the control mode change between the first control mode and the second control mode is performed.

According to the first aspect of the present invention, the intake valve can be prevented from being closed near the bottom dead center, since the first control mode or the second control mode is selected, depending on a particular load state of the internal-combustion engine.

According to the invention, therefore, it is possible to appropriately control the operating state of the internal-combustion engine while properly avoiding knock.

According to the second aspect of the present invention, improvement of fuel efficiency by reduction of pumping loss can be realized while properly avoiding knock.

According to the third aspect of the present invention, the intake valve control appropriate for improving fuel efficiency can be realized in the high-load region while properly avoiding knock.

According to the fourth aspect of the present invention, while properly avoiding knock, the intake valve control appropriate for improving fuel efficiency can be selected depending on the load state of the internal-combustion engine.

According to the fifth aspect of the present invention, while properly avoiding knock, the intake valve control appropriate for improving fuel efficiency can be realized in a low-speed high-load region that is a region in which knock is most likely to occur.

According to the sixth aspect of the present invention, the appropriate control mode can be selected so that the intake valve control optimal in terms of fuel efficiency is used more reliably in accordance with current engine speed.

According to the seventh aspect of the present invention, operation in which the intake air amount is controlled by the certain torque control means while the closing timing of the intake valve is being fully retarded using the intake closing retardation control is possible in the high-load region where the second control mode is selected.

According to the eighth aspect of the present invention, the angle of the throttle valve can be appropriately set when the throttle valve is used as the torque control means in the second control mode.

According to the ninth aspect of the present invention, changes in torque, coupled with the selection of the first control mode or the second control mode, can be appropriately suppressed.

According to the tenth aspect of the present invention, changes in torque due to deterioration of combustion during the control mode selection can be properly suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram explaining a configuration of an internal-combustion engine according to the first embodiment of the present invention.

FIG. 2 is a diagram explaining a configuration of the intake variable valve mechanism that the system shown in

FIG. 1 equips.

FIGS. 3A and 3B are schematic diagrams illustrating how the intake valve is driven by the cam.

FIG. 4 is a schematic diagram illustrating the relationship among the engine speed and torque (load) of the internal-combustion engine and the drive modes of the cam.

FIG. 5 is a schematic diagram illustrating the details of two cams that are provided for the camshaft.

FIG. 6 is a diagram explaining the technique used in the first embodiment of the present invention in order to control the closing timing of the intake valve.

FIGS. 7A and 7B are diagrams showing an example of opening/closing timing of the intake valve used in the variable IVC timing control.

FIG. 8 is a diagram showing the opening/closing timing of the intake valve that is liable to cause knock during the variable IVC timing control.

FIG. 9 is a flowchart illustrating a routine that is executed in the first embodiment of the present invention.

FIG. 10 is a diagram explaining the opening/closing timing of the intake valve used as the second control mode in a second embodiment of the present invention.

FIG. 11 is a diagram explaining an operating region in which the use of the intake valve closing retardation control becomes effective for improving fuel efficiency.

FIG. 12 is a flowchart illustrating a routine that is executed in the second embodiment of the present invention.

FIG. 13 is a flowchart illustrating a routine that is executed in the third embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment System Configuration

FIG. 1 is a diagram explaining a configuration of an internal-combustion engine 10 according to a first embodiment of the present invention. The system of the present embodiment includes the internal-combustion engine 10. Also, the present embodiment assumes an inline four-cylinder engine as the internal-combustion engine 10. Each of cylinders of the internal-combustion engine 10 contains a piston 12. Each of the cylinders of the internal-combustion engine 10 has a combustion chamber 14 formed atop the piston 12. An air intake passageway 16 and an exhaust passageway 18 are communicated with the combustion chamber 14.

An air flow meter 20 is installed near the inlet of the air intake passageway 16 to output a signal representing the flow rate of the air taken into the air intake passageway 16. A throttle valve 22 is installed downstream of the air flow meter 20. The throttle valve 22 is an electronically controlled throttle valve that can control an open position of the throttle valve independently of an open position of an accelerator. A throttle position sensor 24 that detects an open position TA of the throttle is disposed near the throttle valve 22.

A fuel injection valve 26 for injecting a fuel into an air intake port is disposed downstream with respect to the throttle valve 22. At cylinder head of the internal-combustion engine, an ignition plug 28 is mounted for each cylinder in such a form as to project from an upper section of the combustion chamber 14 into the combustion chamber 14. An intake valve 30 and an exhaust valve 32 are provided at the air intake port and an exhaust port, respectively. The intake valve 30 establishes continuity or discontinuity between the combustion chamber 14 and the air intake passageway 16, and the exhaust valve 32 establishes continuity or discontinuity between the combustion chamber 14 and the exhaust passageway 18.

The intake valve 30 and the exhaust valve 32 are driven by an intake variable valve mechanism 34 and an exhaust variable valve mechanism 36, respectively. The detailed configurations of the intake variable valve mechanism 34 and the exhaust variable valve mechanism 36 will be described later with reference to FIGS. 2 to 5.

The system shown in FIG. 1 also includes an electronic control unit (ECU) 40. In addition to the various sensors described above, a crank angle sensor 42 for detecting engine speed, and accelerator opening sensor 44 for detecting accelerator opening PA are electrically connected to the ECU 40. Furthermore, the various actuators described above are electrically connected to the ECU 40. The ECU 40 can control an operational state of the internal-combustion engine 10 on the basis of outputs of the various sensors.

Configuration of the Variable Valve Mechanism According to First Embodiment

FIG. 2 is a diagram explaining a configuration of the intake variable valve mechanism 34 that the system shown in FIG. 1 equips. Hereinafter, the details of the intake variable valve mechanism 34 will be further described with reference to this diagram. Since the exhaust variable valve mechanism 36 is almost the same configuration as the intake variable valve mechanism 34, the details of the drawing and description of the exhaust variable valve mechanism 36 is omitted.

As shown in FIG. 2, each cylinder of the internal-combustion engine 10 is equipped with two intake valves 30. As described above, the internal-combustion engine 10 has four cylinders (cylinders #1 to #4). The explosion stroke is sequentially performed in cylinders #1, #3, #4, and #2 in the order named. The intake variable valve mechanism 34 includes two valve mechanisms (namely intake variable valve mechanism 34A and variable valve mechanism 34B). The intake variable valve mechanism 34A drives the intake valves 30 for cylinders #2 and #3. The variable valve mechanism 34B drives the intake valves 30 for cylinders #1 and #4.

The intake variable valve mechanism 34A includes an electric motor (hereinafter referred to as a motor) 50A, which serves as a driving source, a gear train 52A, which serves as a mechanism for transmitting the rotary motion of the motor 50A, and a camshaft 54A, which converts the rotary motion transmitted from the gear train to a linear open/close motion of the intake valve 30. Similarly, the intake variable valve mechanism 34B includes a motor 50B, a gear train 52B, and a camshaft 54B.

The motors 50A, 50B are servomotors whose rotation speed and rotation amount of the motors 50A, 50B are controllable. A DC brushless or like motor is preferably used as the motors 50A, 50B. The motors 50A, 50B include a resolver, rotary encoder, or other built-in rotation angle sensor that detects their rotation position (rotation angle). The rotation speed and rotation amount of the motors 50A, 50B are controlled by ECU 40.

A cam drive gear 56 and a cam 58 are installed on the periphery of the camshafts 54A, 54B, respectively. The cam drive gear 56 and cam 58 both rotate together with the camshafts 54A, 54B.

The gear train 52A may be configured so that the motor gear 62A, which is installed over an output shaft 60 of the motor 50A, and camshaft 54A rotate via an intermediate gear 64A at the same speed or configured so that the cam drive gear 56 rotates at a higher speed or at a lower speed than the motor gear 62A. Similarly, the gear train 52B transmits the rotation of a motor gear 62B, which is installed over an output shaft of the motor 50B, to the cam drive gear 56 on the camshaft 54B via an intermediate gear 64B (not shown in FIG. 2).

As shown in FIG. 2, the camshaft 54A is positioned over the intake valves 30 for cylinders #2 and #3. The intake valves 30 for cylinders #2 and #3 are opened/closed by cam 58 that is installed on the camshaft 54A. The camshaft 54B, which is separated into two sections, is positioned above the intake valves 30 for cylinders #1 and #4. The intake valves 30 for cylinders #1 and #4 are opened/closed by cam 58 that are installed on the camshaft 54B. The two sections of the camshaft 54B rotate together because they are connected via a coupling member, which is inserted into the hollow camshaft 54A.

FIGS. 3A and 3B are schematic diagrams illustrating how the intake valve 30 is driven by the cam 58. The cam 58 is formed as a plate cam whose nose 58 a is formed by bulging a part of a circular base circle 58 b coaxial with the camshafts 54A, 54B outward in radial direction. The cam 58 is profiled so that its entire circumference does not have negative curvature, that is, a convex curve is drawn outward in radial direction. In the present embodiment, it is shown an example of the direct-driving valve mechanism which the cam 58 drives the intake valve 30 directly. However, the valve mechanism which a cam drives an intake valve via a rocker arm may alternatively be used. If the valve mechanism which the cam drives the intake valve via the rocker arm is used, the cam may be profiled so that a reentrant curve is drawn outward in radial direction.

As shown in FIG. 2, each intake valve 30 includes a valve stem 30 a. Each cam 58 faces a valve lifter 66, which is positioned at one end of the valve stem 30 a for the intake valve 30. Compressive reaction force of a valve spring (not shown) pushes each intake valve 30 toward the cam 58. Therefore, if the valve lifter 66 faces the base circle 58 b of the cam 58, the intake valve 30 comes into close contact with a valve sheet (not shown) of the intake port by the force of the valve spring, thereby closing the intake port.

When the rotary motions of the motors 50A, 50B are transmitted to the camshafts 54A, 54B through the gear trains 52A, 52B, the cam 58 rotates together with the camshafts 54A, 54B. The valve lifter 66 is pressed downward as the nose 58 a climbs over the valve lifter 66. The intake valve 30 then opens/closes against the force of the valve spring.

FIGS. 3A and 3B also indicate two drive modes for the cam 58: normal rotation drive mode and swing drive mode. In the normal rotation drive mode, the motors 50A, 50B continuously rotate in one direction to rotate the cam 58 continuously in the direction of normal rotation (in the direction indicated by the arrow in FIG. 3A) beyond a maximum lift position as indicated in FIG. 3A, that is, a position at which the nose 58 a of the cam 58 comes into contact with a mating part (the valve lifter 66 in this case). In the swing drive mode, on the other hand, the cam 58 is caused to reciprocate as shown in FIG. 3B by changing the rotation direction of the motors 50 a, 50B before the maximum lift position for the normal rotation drive mode is reached.

In the normal rotation drive mode, the operating angle of the intake valve 30 is controlled by controlling the rotation speed of the cam 58. In the swing drive mode, the operating angle and lift amount of the intake valve 30 can be controlled by controlling the rotation speed of the cam 58 and swing angle range of the cam 58. In this way, according to the intake variable valve mechanism 34, the intake valve 30 can be driven while the operating angle and lift amount (valve-opening characteristics) are optimized in accordance with the operating state.

FIG. 4 is a schematic diagram illustrating the relationship among the engine speed and torque (load) of the internal-combustion engine 10 and the drive modes of the cam 58. The drive modes of the cam 58 are selectively used in association with the engine speed and torque (load). In a low engine speed region, the swing drive mode is basically selected. In a high engine speed region, on the other hand, the normal rotation drive mode is basically selected. Consequently, control is exercised so as to decrease the operating angle and lift amount of the intake valve 30 in the low engine speed region and increase the operating angle and lift amount of the intake valve 30 in the high engine speed region. As a result, an optimum amount of air can be delivered into an engine cylinder in accordance with the engine speed and torque.

FIG. 5 is a schematic diagram illustrating the details of two cams 58 that are provided for the camshaft 54A. As shown in FIG. 5, the cam 58 for driving the intake valves 30 for cylinder #2 and the cam 58 for driving the intake valves 30 for cylinder #3 are positioned 180 degrees apart. In a four-cylinder internal-combustion engine, cylinders #1, #3, #4, and #2 sequentially perform an explosion stroke in the order named over a crank angle of 720°. Therefore, the intake strokes for cylinders #2 and #3 are performed at intervals of 360° crank angle. The intake variable valve mechanism 34A rotates or swings the camshaft 54A in such a manner that the cam 58 for cylinder #2 and the cam 58 for cylinder #3 alternately drive the intake valves 30 for cylinder #2 and the intake valves 30 for cylinder #3 at intervals of 360° crank angle. Similarly, the camshaft 548 is provided with cams 58 for driving the intake valves 30 for cylinders #1 and #4, and the intake variable valve mechanism 34B drives the intake valves 30 for cylinder #1 and the intake valves 30 for cylinder #4 by rotating or swinging the camshaft 54B.

In the thus-constructed system of the present embodiment, the operating angle of the intake valve 30 can be varied in the normal rotation drive mode by changing the rotation angle of the cam 58 per revolution thereof, more specifically, by changing the rotation speed of the motor 50A, 50B so as to change a period during which the cam 58 is lifting the intake valve 30. In the normal rotation drive mode, a desired operating angle of the intake valve 30 is set in the ECU 40 according to the operating state of the internal-combustion engine 10. The ECU 40 controls the operation of the motor 50A, 50B so that the appropriate motor speed for the desired operating angle can be achieved.

In the swing drive mode, the operating angle and maximum lift amount of the intake valve 30 can be varied by changing the rotation speed and rotation amount of the motor 50A, 50B so as to change the rotation speed of the cam 58 and the angle range in which the cam 58 rocks. In the swing drive mode, a desired operating angle of the intake valve 30 and a desired maximum lift amount thereof are set in the ECU 40 according to the operating state of the internal-combustion engine 10. The ECU 40 controls the operation of the motor 50A, 50B so that the appropriate rotation speed and rotation amount of the motor 50A, 50B according to the desired operating angle and desired maximum lift amount of the intake valve 30 can be achieved.

Feature Portions of the First Embodiment

FIG. 6 is a diagram explaining the technique used in the first embodiment of the present invention in order to control the closing timing of the intake valve 30. Hereinafter, the closing timing of the intake valve 30 is referred to as the IVC (intake valve closing). The waveform shown in FIG. 6 represents a constant operating angle line. Details of the knock information given in FIG. 6 are set forth later in description of the routine shown in FIG. 9.

In the system of the present embodiment, the above-described intake variable valve mechanism 34 and the throttle valve 22 can both be used as an intake air amount controller. The present embodiment controls the intake air amount primarily by controlling the valve-opening characteristics of the intake valve 30 via the intake variable valve mechanism 34.

More specifically, the system of the present embodiment controls the intake air amount as follows to improve fuel efficiency by reducing pumping loss: the IVC timing is advanced by reducing the operating angle of the intake valve 30 to limit the amount of air passed through the intake valve 30, and at the same time, a throttle angle TA is correspondingly increased.

To this end, the desired operating angle of the intake valve 30 is determined according to a load factor requirement and engine speed of the internal-combustion engine 10, and after the determination of the desired operating angle, the opening/closing timing of the intake valve 30 is determined to achieve the determined operating angle in an appropriate valve-opening phase. Controlling the intake air amount in this manner renders the operating angle variable according to the load (load factor) and engine speed of the internal-combustion engine 10, thus controlling the IVC timing of the intake valve 30. More specifically, as shown in FIG. 6, as the load factor and the engine speed increase, the operating angle is gradually increased and the IVC timing of the intake valve 30 is gradually retarded.

The control performed in this way to make the IVC timing of the intake valve 30 variable and adjust the intake air amount according to the load is termed “IVC variable control” hereinafter.

FIGS. 7A and 7B are diagrams showing an example of opening/closing timing of the intake valve 30 used in the variable IVC timing control. FIG. 7A shows the timing in which the intake valve 30 is opened/closed in the low-load region where a small operating angle is selected. In this case, the intake valve 30, after being opened near the top dead center TDC of air intake, is closed at a relatively earlier stage than the timing in which the intake valve is closed near the bottom dead center BDC. FIG. 7B shows the valve timing of the intake valve 30 in the high-load region where a large operating angle is selected. In this case, the intake valve 30, after being opened at the crank position more advanced in angle than the case in FIG. 7A with respect to the top dead center TDC of air intake to obtain a desired valve overlapping period, is closed with a timing delay behind closing near the bottom dead center BDC. This timing delay is provided so that a sufficient amount of air is taken into the cylinder.

For example, for a change from the low-load region to the high-load region during the variable IVC timing control described above, while the throttle angle TA is being basically maintained at a relatively large angle, the IVC timing of the intake valve 30 can be retarded (e.g., during a change from the stage of FIG. 7A, towards the stage of FIG. 7B) according to the load requirement of the internal-combustion engine 10 so that the operating angle gradually increases. Using this control technique allows the intake air amount to be controlled while appropriately reducing pumping loss.

FIG. 8 is a diagram showing the opening/closing timing of the intake valve 30 that is liable to cause knock during the variable IVC timing control described above. If the above variable IVC timing control is executed without any consideration given to the IVC timing of the intake valve, an operating angle equivalent to the very timing in which the intake valve is closed near the bottom dead center BDC will be used in a medium-load region of about 60% to 70% in load factor, as shown in FIG. 8. In such a medium-load region, partly since the throttle angle is controlled to a relatively large value, if the intake valve is closed within a required angle range close to the bottom dead center BDC of air intake, the actual internal-compression ratio of the cylinder will increase and knock will be more likely to occur.

Accordingly, the present embodiment provides two control modes. One is the first control mode in which the control system basically controls the intake air amount by controlling the IVC timing of the intake valve 30 according to the load by use of the IVC variable control, and then controls the IVC timing of the intake valve 30 at the timing-advancing angle position with respect to the certain angle range inclusive of the bottom dead center BDC of air intake. The other is the second control mode in which the control system controls the IVC timing of the intake valve 30 at the timing-retarding angle position with respect to the above certain angle range inclusive of the bottom dead center BDC of air intake. The first control mode is selected in a region relatively low in load, and the second control mode is selected in a region relatively high in load.

FIG. 9 is a flowchart of the routine which the ECU 40 executes in the present first embodiment to implement the above functionality. In the routine of FIG. 9, a current load factor of the internal-combustion engine 10 is calculated in step 100 first. The load factor is calculated from the accelerator opening, the engine speed, the intake air amount measured by the air flow meter 20, and sensor data such as an intake pipe vacuum pressure.

Next in step 102, the first control mode or the second control mode depending on the current operating state is selected on the basis of the current load factor and the engine speed. Following this step, step 104 is executed to judge whether the selected current control mode is the first control mode.

If it is judged in step 104 that the current control mode is the first control mode, it is next judged in step 106 on the basis of an accelerator opening and an accelerator opening change rate whether a load-increasing request (speed-up request) for a higher load is present. If, as a result, such a load-increasing request is judged to be present, it is judged in step 108 whether the load-increasing request relates to increasing the load from a valve timing region in which knock is likely.

Internal-combustion engines are prone to knock in a low engine speed region, especially, in the load region where the load factor exceeds about 60%. In step 108, therefore, when the IVC variable control is applied, a region (see FIG. 6) of about 50% to 80% in load factor, inclusive of the load region of about 60% to 70% in load factor where knock is most likely, is defined as a “knock-prone valve timing region” to prevent the IVC timing of the intake valve 30 from being controlled to stay exactly within the certain range close to the bottom dead center BDC of air intake. In FIG. 6, the knock-prone valve timing region is set to remain constant, independently of the engine speed. However, the knock-prone valve timing region is not always set to be constant and may be made variable in response to the engine speed or a compression end temperature.

If it is judged in step 108 that the current load-increasing request does not relate to increasing the load from the knock-prone valve timing region, continued use of the first control mode that is the current control mode is determined in step 110. In this case, therefore, the IVC timing of the intake valve 30 is controlled according to the load so as to obtain the intake air amount appropriate for the load.

Conversely if it is judged in step 108 that the current load-increasing request relates to increasing the load from the knock-prone valve timing region, the first control mode that is the current control mode is instantly changed to the second control mode in step 112. More specifically, the intake variable valve mechanism 34 instantly performs a mode change from the first control mode for which the operating angle is set to reach, for example, about 150° CA., to the second control mode for which the operating angle is set to reach, for example, about 210° CA. In that case, throttle angle TA and the ignition timing are next adjusted in step 114 to adjust torque so that the control mode change does not cause a difference in torque.

In the routine of FIG. 9, if it is judged in step 104 that the current control mode is not the first control mode, that is, that the current control mode is the second control mode, it is next judged in step 116 whether a load-reducing request (slowdown request) for a lower load is present on the basis of the accelerator opening, the accelerator opening change rate, and the like. If, as a result, such a load-reducing request is judged to be present, it is judged in step 118 whether the load-reducing request relates to load reduction from the valve timing region in which knock is likely.

If it is judged in step 118 that the current load-reducing request does not relate to load reduction from the knock-prone valve timing region, continued use of the second control mode that is the current control mode is determined in step 120. In this case, therefore, the IVC timing of the intake valve 30 is controlled according to the load so as to obtain the intake air amount appropriate for the load.

Conversely if it is judged in step 118 that the current load-reducing request relates to load reduction from the knock-prone valve timing region, the second control mode that is the current control mode is instantly changed to the first control mode in step 122. More specifically, the intake variable valve mechanism 34 instantly performs a mode change from the second control mode for which the operating angle is set to become about 210° CA., for example, to the first control mode for which the operating angle is set to become about 150° CA., for example. In that case, throttle angle TA and the ignition timing are next adjusted in step 124 to adjust torque so that the control mode change does not cause a difference in torque.

According to the above-described routine of FIG. 9, when the current load region of the internal-combustion engine 10 enters the knock-prone valve timing region, if a load change request is present, the IVC timing of the intake valve 30 is controlled to prevent the valve from being closed near the bottom dead center BDC of air intake. In addition, in the intake variable valve mechanism 34 according to the present embodiment, the selection of the first or second control mode for such control can be instantly performed for each cycle of the internal-combustion engine 10. According to processing of the above routine, during the control mode change in the load region where knock is liable to occur, the IVC timing of the intake valve 30 can always be controlled so that the closing timing near the air intake bottom dead center BDC is not used. In this way, the system of the present embodiment allows the operating state of the internal-combustion engine 10 to be appropriately controlled using the intake air amount control based on the IVC variable control which provides high fuel-saving performance while properly avoiding the occurrence of knock.

In the first embodiment, which has been described above, the “intake valve control means” according to the first aspect of the present invention is implemented when the ECU 40 performs step 110, 112, 120, or 122; the “control mode selection means” according to the first aspect of the present invention is implemented when the ECU 40 performs step 102, 108, or 118.

Second Embodiment

A second embodiment of the present invention will now be described with reference to FIGS. 10 to 12.

The system according to the second embodiment is implemented by adopting the hardware configuration shown in FIG. 1 and allowing the ECU 40 to execute a routine shown in FIG. 12 instead of the routine shown in FIG. 9.

Feature Portions of the Second Embodiment

FIG. 10 is a diagram explaining the opening/closing timing of the intake valve 30 used as the second control mode in a second embodiment of the present invention. FIG. 10 shows an example in which, in addition to being opened at a position relatively advanced in angle with respect to the top dead center TDC of air intake, the intake valve 30 has its IVC timing fully retarded to such an extent that blowback of the intake air into the intake passage intentionally occurs to lower an actual compression ratio.

The IVC timing here of such an extent that the blowback of the intake air intentionally occurs refers to IVC timing in which the intake air is blown back under a steady state obtained after the engine has reached a desired operating state with the intake valve controlled to be closed in the particular IVC timing. More specifically, the above IVC timing refers to the IVC timing retarded more than the IVC timing (e.g., 30° to 40° CA. ABDC) that is adopted for high-speed high-load operation to ensure that desired output is obtained in a general internal-combustion engine. Even more specifically, the above IVC timing refers to, for example, IVC timing of 80° to 100° CA. ABDC being inclusive of 90° CA. ABDC shown in FIG. 10.

Hereinafter, the above second control mode used in the present embodiment, that is, the IVC timing control of the intake valve 30 that aims at achieving Atkinson-cycle engine performance based on delayed closing of the intake valve 30 is also termed the “intake valve closing retardation control”. More specifically, during execution of the intake valve closing retardation control, the IVC timing of the intake valve 30 is controlled to the certain IVC timing fully retarded in the foregoing manner, and then the intake air amount is controlled by the throttle valve 22. In addition, the IVC timing of the intake valve 30 during the execution of the intake valve closing retardation control may not be fixed. Instead, the IVC timing may be made variable according to the load, engine speed, and/or other parameters concerning the operating state.

Differences between the intake valve closing retardation control and the IVC variable control in the foregoing first embodiment are defined below. The IVC variable control is a technique for controlling the intake air amount by, while fully increasing the throttle angle TA, controlling the IVC timing of the intake valve 30 so that the intake valve 30 is closed at a right timing when a desired intake air amount is judged to be obtainable according to the load and/or engine speed. In the first embodiment using the IVC variable control as the first control mode and as the second control mode, therefore, under a transient state existing immediately after the mode change from the first control mode to the second control mode has been performed following receipt of a load-increasing request, the blowback of the intake air may temporarily occur, even during the use of the IVC variable control. The IVC variable control, however, will differ from the intake valve closing retardation control intended to blow back the intake air during a steady state.

FIG. 11 is a diagram explaining an operating region in which the use of the intake valve closing retardation control becomes effective for improving fuel efficiency. A low-speed high-load region provided with hatching in FIG. 11 denotes the region in which the intake valve closing retardation control excels the IVC variable control in fuel efficiency. There are two reasons why the intake valve closing retardation control excels the IVC variable control in the low-speed high-load region. One reason is that although both kinds of control are equal in pumping loss, the intake valve closing retardation control is advantageous in that this control can bring about decreases in cooling loss (i.e., decreases in combustion temperature), coupled with increases in exhaust gas recirculation (EGR) gas amount due to increases in the valve overlapping period near the top dead center TDC of air intake. The other reason is that the intake valve closing retardation control can contribute to improvement of an in-cylinder fuel-air mixture distribution due to a long-lasting flow of intake air, and to improvement of combustion due to increases in intake air disturbance.

Conversely, in regions other than the hatched region in FIG. 11, the IVC variable control excels the intake valve closing retardation control in fuel efficiency. The reasons why the IVC variable control excels in fuel efficiency in a low-speed low-load region, in particular, are described below. That is to say, one reason is that when the intake valve closing retardation control is used, since the intake air that has been heated by heat exchange with the intake valve 30, a wall surface of a combustion chamber 14, or the like, during the intake of the air to the cylinder, is blown back into the intake passage, the compression end temperature is not easy to fully increase. One reason is that since a compression period of the intake air is short (the actual compression ratio based on retarded closing is small), the compression end temperature is not easy to fully increase. One reason is that the low-speed low-load region is originally a region that is severe about obtaining the appropriate combustion. For these reasons, in the low-speed low-load region, the IVC variable control excels in fuel efficiency since combustion improves.

As shown in FIG. 11, when a comparison is performed between engine speed regions of, about 2,500 rpm or less (as one example), the region in which the intake valve closing retardation control excels in fuel efficiency extends down to a load side lower than a region in which knock is likely. Accordingly, the present embodiment is constructed so that during the IVC variable control, when a load-increasing request is given in a region not exceeding a certain engine speed (in the example of FIG. 11, about 2,500 rpm), the control mode is changed from the IVC variable control to the intake valve closing retardation control, in accordance with a fuel efficiency improvement request as necessary. More specifically, the closing timing of the intake valve 30 (i.e., the IVC timing) and opening timing thereof (i.e., IVO timing) are instantly changed over so that the IVC timing of the intake valve 30 that has been controlled to such an extent that the operating angle becomes, for example, 280° CA. (about 80° CA. ABDC) can be obtained immediately after the IVC timing has been controlled to such an extent that the operating angle becomes, for example, 140° CA. (about 40° CA. BBDC).

In the present embodiment, in a region of medium engine speeds higher than the above certain engine speed, that is, if a knock-prone region extends down to a load side lower than the region in which the intake valve closing retardation control excels in fuel efficiency, the control mode is also changed from the IVC variable control to the intake valve closing retardation control, in accordance with knock avoidance request as necessary. More specifically, the IVC timing and IVO timing of the intake valve 30 are instantly changed over so that the IVC timing that has been controlled to such an extent that the operating angle becomes, for example, 280° CA. (about 80° CA. ABDC) can be obtained immediately after the IVC timing has been controlled to such an extent that the operating angle becomes, for example, 160° CA. (about 20° CA. BBDC).

FIG. 12 is a flowchart of a routine which the ECU 40 executes in the second embodiment in order to implement the above functionality. The routine in FIG. 12 assumes the control in a region not exceeding a certain engine speed (3,000 rpm in the example of FIG. 11). This routine may likewise be applied at other higher engine speeds. Alternatively, in a region of higher engine speeds, substantially the same routine as that of FIG. 9 in the foregoing first embodiment may be executed during the use of the second control mode as the IVC variable control. In FIG. 12, the same steps as those shown in FIG. 9 for the first embodiment are each assigned the same reference number or symbol, and description of these steps is omitted or simplified below.

In the routine of FIG. 12, after a current load factor of the internal-combustion engine 10 was calculated in step 100, the first or second control mode depending on the current operating state is selected in step 200 on the basis of the current load factor and engine speed. In this routine, the IVC variable control is used in the first control mode and the intake valve closing retardation control is used in the second control mode.

In the routine of FIG. 12, if in step 104, the current control mode is judged to be the first control mode, and in step 106, a load-increasing request is judged to be present, a discrimination is next performed in step 202 to examine whether the current load-increasing request is a request for a load increase toward the region in which the intake valve closing retardation control excels in fuel efficiency. Such a relationship as shown in FIG. 11, that is, a relationship in which the region in which the intake valve closing retardation control excels in fuel efficiency is shown within the operating region represented by the load factor and the engine speed is stored within the ECU 40. This relationship and the current load-increasing request are compared with each other and the process of step 202 is executed.

If, in step 202, the load-increasing request is judged not to be a request for a load increase toward the region in which the intake valve closing retardation control excels in fuel efficiency, whether the current load-increasing request is a request for a load increase from the knock-prone valve timing region is next discriminated in step 108. As a result, if the judgment criterion in step 108 does not hold, the use of the first control mode which is the current control mode is continued intact in step 110.

If the judgment criterion in step 108 holds, the first control mode that is the current control mode is changed to the second control mode instantly in step 204. More specifically, the intake variable valve mechanism 34 instantly performs a mode change from the first control mode for which the operating angle is set to become about 160° CA., for example, to the second control mode for which the operating angle is set to become about 280° CA., for example. In that case, torque control with the throttle valve 22 is selected and the ignition timing is changed in synchronization with the control mode change. Also, throttle angle TA and the ignition timing are adjusted in step 206 to adjust torque so that the control mode change does not cause a difference in torque.

If, in step 202, the load-increasing request is judged to be a request for a load increase toward the region in which the intake valve closing retardation control excels in fuel efficiency, the first control mode that is the current control mode is changed to the second control mode instantly in step 208. More specifically, the intake variable valve mechanism 34 instantly performs a mode change from the first control mode for which the operating angle is set to become about 140° CA., for example, to the second control mode for which the operating angle is set to become about 280° CA., for example. In that case, torque control with the throttle valve 22 is selected and the ignition timing is changed in synchronization with the control mode change. Also, throttle angle TA and the ignition timing are adjusted in step 210 to adjust torque so that the control mode change does not cause a difference in torque.

In the routine of FIG. 12, if in step 104, the current control mode is judged to be the second control mode, and in step 116, a load-decreasing request is judged to be present, it is next discriminated in step 212 to examine whether the current load-increasing request is a request for load reduction to the region in which the intake valve closing retardation control excels in fuel efficiency.

If, in step 212, the current load-decreasing request is judged to be a request for load reduction to the region in which the intake valve closing retardation control excels in fuel efficiency, the use of the second control mode which is the current control mode is continued intact in step 214.

Conversely, if it is judged in step 212 that the current load-decreasing request is not a request for load reduction to the region in which the intake valve closing retardation control excels in fuel efficiency, that is, if the current load-increasing request is judged to be a request for load reduction to the region in which the IVC variable control excels in fuel efficiency, the second control mode that is the current control mode is changed to the first control mode instantly in step 216. More specifically, the intake variable valve mechanism 34 instantly performs a mode change from the second control mode for which the operating angle is set to become about 280° CA., for example, to the first control mode for which the operating angle is set to become about 140° to 160° CA., for example, depending on the engine speed. In that case, torque control with the throttle valve 22 is selected and the ignition timing is changed in synchronization with the control mode change. Also, throttle angle TA and the ignition timing are adjusted in step 218 to adjust torque so that the control mode change does not cause a difference in torque.

According to the above-described routine of FIG. 12, when a load change is requested that spans the region in which the IVC variable control excels in fuel efficiency, and the region in which the intake valve closing retardation control excels in fuel efficiency, the intake variable valve mechanism 34 is used to instantly perform a mode change between the first control mode which uses the IVC variable control, and the second control mode which uses the intake valve closing retardation control. Use of such control makes it possible, even near a load region in which knock is likely, to always control the IVC timing of the intake valve 30 so that the closing timing near the air intake bottom dead center BDC is not used, during the control mode change. In addition, in the present embodiment, the intake valve closing retardation control in which the IVC timing of the intake valve 30 is retarded more significantly than during the IVC variable control is used as the second control mode at a higher-load side. Accordingly, the system of the present embodiment allows the implementation of the intake air amount control which, while properly avoiding the occurrence of knock, yields high fuel efficiency, compared with that obtained by using the system of the first embodiment.

In addition, as shown in FIG. 11, a boundary line between the region in which the intake valve closing retardation control excels in fuel efficiency, and the region in which the IVC variable control excels in fuel efficiency, shifts toward the higher-load region as the engine speed increases. In the routine of FIG. 12, whether the current load-changing request requires a control mode change is discriminated in step 202, 212, with the relationship of FIG. 11 taken into account. Under such control, in a region of certain low engine speeds, the change from the IVC variable control to the intake valve closing retardation control is not performed until the load region of the internal-combustion engine has reached the higher region as engine speed increases, conversely, the change from the intake valve closing retardation control to the IVC variable control is not performed until the load region of the internal-combustion engine has reached the lower region as engine speed increases. These mean that the appropriate control mode can be selected so that the control optimal in terms of fuel efficiency can be used more reliably depending on the current engine speed.

In the second embodiment, which has been described above, the throttle valve 22 corresponds to the “torque control means” according to the seventh aspect of the present invention; the “torque control change means” according to the seventh aspect of the present invention is implemented when the ECU 40 performs step 206, 210, or 218.

Further, in the second embodiment, which has been described above, the “ignition timing change means” according to the ninth aspect of the present invention is implemented when the ECU 40 performs step 206, 210, or 218.

Third Embodiment

A third embodiment of the present invention will now be described with reference to FIG. 13.

The system according to the third embodiment is implemented by adopting the hardware configuration shown in FIG. 1 and allowing the ECU 40 to execute a routine shown in FIG. 13 instead of the routine shown in FIG. 12.

Feature Portions of the Third Embodiment

The system of the present embodiment is characterized in a technique relating to the torque adjustments performed when the control mode is instantly changed between the IVC variable control and the intake valve closing retardation control (the torque adjustments are detailed in step 300 and the like). More specifically, the present embodiment adjusts a change range of throttle angle TA on the basis of the IVC timing and operating angle of the intake valve 30 existing after the control mode change.

When the intake valve closing retardation control that uses such opening/closing timing of the intake valve 30 as shown in FIG. 10 is executed, advancing the opening timing of the intake valve (i.e., the IVO timing) increases the valve overlapping period, thus increasing an internal EGR gas amount. The appropriate increase in internal EGR gas amount offers a fuel efficiency improvement effect, but slightly deteriorates combustion. In the present embodiment, therefore, the ignition timing is changed in synchronization with the control mode change. Additionally, the amount of ignition timing advanced after the control mode change has been performed is adjusted in accordance with the valve overlapping period (the IVO timing of the intake valve 30). More specifically, the ignition timing is advanced more significantly as the valve overlapping period becomes longer.

FIG. 13 is a flowchart of a routine which the ECU 40 executes in the third embodiment in order to implement the above functionality. The routine of the FIG. 13 is similar in content to the routine of the FIG. 12 except that steps 206, 210, and 218 are replaced by steps 300, 302, and 304, respectively. Therefore, as regards the steps in FIG. 13 that are the same as those in FIG. 12, which illustrates the second embodiment, their description is omitted or abridged with the same reference numerals assigned. Further, the present routine is obtained by combining the routine of the FIG. 12 and the torque-adjusting method in the present embodiment. But, alternatively, the torque-adjusting method may be combined with the routine of the FIG. 9 in the above-described first embodiment.

In the routine of FIG. 13, if in step 108, the current load-increasing request is judged to be a request for a load increase from the knock-prone valve timing region, and in step 204, the control mode change from the first control mode that is the current control mode, to the second control mode, is instantly performed, throttle angle TA and the ignition timing are next adjusted in step 300 to adjust torque so that the control mode change does not cause a difference in torque.

A map (not shown) in which variations in throttle angle TA are predefined in the relationship between the IVC timing and operating angle of the intake valve 30, obtained after the control mode change has been performed is stored within the ECU 40. The ECU 40 refers to this map and adjusts the throttle angle TA existing after the control mode change. A map (not shown) in which the amount of advancement of the ignition timing is predefined in the relationship with the valve overlapping period (or the IVO timing of the intake valve 30) existing after the control mode change, is also stored within the ECU 40. The ECU 40 refers to this map and adjusts the amount of advancement of the ignition timing, obtained after the control mode change.

In the routine of FIG. 13, substantially the same steps 302, 304 as step 300 are executed, but since the process executed in steps 302, 304 are substantially the same as the process performed in step 300, detailed description of this process are omitted.

According to the above-described routine of FIG. 13, the throttle angle after the control mode change can be appropriately adjusted in accordance with the relationship established between the IVC timing and operating angle of the intake valve 30 after the control mode change. In addition, according to the above routine, the amount of ignition timing advanced after the control mode change can be appropriately adjusted for improved fuel economy in accordance with the relationship established with respect to the valve overlapping period after the control mode change. Accordingly, the system of the present embodiment makes it possible to properly suppress differences in the torque of the internal-combustion engine 10 due to the control mode change.

In the first to third embodiments described above, the cam shaft 54A, 54B is driven by the motor 50A, 50B of the intake variable valve mechanism 34 in order to drive the opening/closing of the intake valve 30 of each cylinder. However, the variable valve mechanism that at least makes the IVC timing of the intake valve variable in the present invention may not always be limited to or by such a configuration. Instead, the variable valve mechanism may employ, for example, electromagnetic driving valve actuator to drive the intake valve by electromagnetic force. Alternatively, the variable valve mechanism may be of a mechanical scheme, provided that the mechanism has a function to continuously change the IVC timing of the intake valve in at least the first control mode, and that the first control mode or the second control mode can be instantly selected by, for example, engaging or disengaging coupling of the pin. 

1-3. (canceled)
 4. A control apparatus for an internal-combustion engine having a variable valve mechanism which at least makes closing timing of an intake valve variable, the control apparatus comprising: intake valve control means with a first control mode for controlling the closing timing of the intake valve at an angle-advancing side relative to a certain range including an air intake bottom dead center, in which knock is more likely to occur, and with a second control mode for controlling the closing timing of the intake valve at an angle-retarding side relative to the certain range, wherein the intake valve control means controls the closing timing of the intake valve in either the first control mode or the second control mode; and control mode selection means for selecting the first control mode for operation in a region of relatively low loads, and selecting the second control mode for operation in a region of relatively high loads; wherein the first control mode is the control that determines the closing timing of the intake valve according to a load of the internal-combustion engine; wherein the closing timing of the intake valve is retarded to an angle side nearer the air intake bottom dead center as the load of the internal-combustion engine increases; wherein the control mode selection means changes the first control mode, if the load of the internal-combustion engine has become high until such an extent that the closing timing of the intake valve is likely to enter the certain range where knock is more likely to occur, to the second control mode that controls the closing timing of the intake valve at the angle-retarding side relative to the air intake bottom dead center and at the angle-retarding side relative to the certain range where knock is more likely to occur; wherein the second control mode is the intake valve closing retardation control that determines the closing timing of the intake valve such that even under a steady state, blowback of intake air into an intake passage occurs; wherein a load region in which the intake valve closing retardation control excels the first control mode in fuel efficiency is set, in a low engine speed region in which the engine runs at a speed equal to or smaller than a certain value, so as to extend down to a load side lower than a region in which knock is likely to occur; and wherein the control mode selection means changes the first control mode to the second control mode, in the low engine speed region, when it is judged that the intake valve closing retardation control excels the first control mode in fuel efficiency.
 5. The control apparatus for an internal-combustion engine having a variable valve mechanism according to claim 4, wherein the intake valve closing retardation control is used in an operating region in which the engine runs at a speed equal to or smaller than a certain value and under a load equal to or greater than a certain value.
 6. The control apparatus for an internal-combustion engine having a variable valve mechanism according to claim 4, wherein the control mode selection means selects the first control mode until the load region of the internal-combustion engine has reached the higher region as engine speed increases.
 7. The control apparatus for an internal-combustion engine having a variable valve mechanism according to claim 4, the control apparatus further comprising: torque control means for controlling a torque of the internal-combustion engine in addition to controlling the closing timing control of the intake valve via the intake valve control means; and torque control change means for, when the second control mode is selected by the control mode selection means, changing the torque control performed by the intake valve control means, to the torque control performed by the torque control means.
 8. The control apparatus for an internal-combustion engine having a variable valve mechanism according to claim 7, wherein the torque control means is a throttle valve that controls an intake air amount, wherein the torque control means adjusts an open position of the throttle valve in accordance with at least the closing timing of the intake valve, of the closing timing and operating angle of the intake valve existing when the first control mode is changed to the second control mode.
 9. The control apparatus for an internal-combustion engine having a variable valve mechanism according to claim 4, the control apparatus further comprising: ignition timing change means for changing ignition timing of the internal-combustion engine in synchronization with the control mode change between the first control mode and the second control mode.
 10. The control apparatus for an internal-combustion engine having a variable valve mechanism according to claim 9, wherein the ignition timing change means determines an advancing amount of the ignition timing in accordance with a valve overlapping period existing when the control mode change between the first control mode and the second control mode is performed.
 11. A control apparatus for an internal-combustion engine having a variable valve mechanism which at least makes closing timing of an intake valve variable, the control apparatus comprising: an intake valve control device with a first control mode for controlling the closing timing of the intake valve at an angle-advancing side relative to a certain range including an air intake bottom dead center, in which knock is more likely to occur, and with a second control mode for controlling the closing timing of the intake valve at an angle-retarding side relative to the certain range, wherein the intake valve control device controls the closing timing of the intake valve in either the first control mode or the second control mode; and a control mode selection device for selecting the first control mode for operation in a region of relatively low loads, and selecting the second control mode for operation in a region of relatively high loads; wherein the first control mode is the control that determines the closing timing of the intake valve according to a load of the internal-combustion engine; wherein the closing timing of the intake valve is retarded to an angle side nearer the air intake bottom dead center as the load of the internal-combustion engine increases; wherein the control mode selection device changes the first control mode, if the load of the internal-combustion engine has become high until such an extent that the closing timing of the intake valve is likely to enter the certain range where knock is more likely to occur, to the second control mode that controls the closing timing of the intake valve at the angle-retarding side relative to the air intake bottom dead center and at the angle-retarding side relative to the certain range where knock is more likely to occur; wherein the second control mode is the intake valve closing retardation control that determines the closing timing of the intake valve such that even under a steady state, blowback of intake air into an intake passage occurs; wherein a load region in which the intake valve closing retardation control excels the first control mode in fuel efficiency is set, in a low engine speed region in which the engine runs at a speed equal to or smaller than a certain value, so as to extend down to a load side lower than a region in which knock is likely to occur; and wherein the control mode selection device changes the first control mode to the second control mode, in the low engine speed region, when it is judged that the intake valve closing retardation control excels the first control mode in fuel efficiency. 